1. Field of the Invention
The present invention relates to a cutting tool having a cutting member comprising a coated carbide alloy (hereinafter referred to as "coated carbide cutting member") wherein a thick, uniform Al.sub.2 O.sub.3 -based layer consisting essentially of aluminum oxide (hereinafter Al.sub.2 O.sub.3) is formed as a hard coating layer. The cutting member exhibits no chipping in continuous and interrupted cutting of metal, such as steel or cast iron, and exhibits stable cutting ability for long periods.
2. Discussion of the Background
Coated carbide cutting members are known in which the cutting members comprise a cemented carbide substrate (hereinafter carbide substrate) and hard coating layers comprising an Al.sub.2 O.sub.3 layer and at least one layer, for example, selected from the group consisting of a titanium carbide (TiC) layer, a titanium nitride (TiN) layer, a titanium carbonitride (TiCN) layer, a titanium oxide (TiO.sub.2) layer, a titanium carboxide (TiCO) layer, a titanium nitroxide (TiNO) layer, and a titanium carbonitroxide (TiCNO) layer, and where the hard coating layers are formed by chemical and/or physical vapor deposition and have an overall average thickness of 3 to 20 .mu.m.
Further, it is also known to form the Al.sub.2 O.sub.3 layer composing the hard coating layer from a reactive gas comprising
1 to 20 percent by volume of aluminum trichloride (AlCl.sub.3), PA1 0.5 to 30 percent by volume of carbon dioxide (CO.sub.2), PA1 1 to 30 percent by volume of carbon monoxide (CO) or hydrogen chloride (HCl) if necessary, and PA1 the balance being hydrogen, PA1 and a method for its production.
at a reaction temperature of 950 to 1,100.degree. C. and an atmospheric pressure of 20 to 200 torr.
Recently, highly durable coated carbide cutting members have been in demand due to the promotion of factory automation and labor saving in cutting. Among hard coating layers, thickening of the Al.sub.2 O.sub.3 layer which provides excellent resistance against oxidation, thermal stability and high hardness, has been investigated in response to such demands. However, it is inevitable that the Al.sub.2 O.sub.3 layer creates local nonuniformities in conventional deposition processes for thickening, and the resulting cutting members have significant nonuniformity in thickness between the flank, rake and edge (the cross of the flank and the rake). When such cutting members are used for the interrupted cutting of steel and cast iron, the cutting tool easily chips, resulting in a relatively short lifetime for the cutting tool.